For some laser processing operations it is known to divide a laser beam into two partial beams, and then to focus the partial beams separately onto a workpiece.
It is current practice to mount roof mirrors to the laser welding systems at the so-called C axis. This means that a rotation about the so-called B axis produces a relative motion between roof mirror and focusing mirror that, in turn, means a change of orientation of the two focuses. Moreover, in such cases it is typically necessary to remove an adaptive mirror when a roof mirror is being used, which renders automatic adjustment of the focal position impossible.
So-called bifocal mirrors are also already being used for processing three-dimensional workpieces. The double focus is realized with a focusing mirror having two different parabolic surfaces. The manufacture of these bifocal mirrors can be very expensive, and the focuses typically must be oriented in only one direction due to production specifications.